1. Field of the Invention
Aspects of the present invention relate to a battery pack, and more particularly to, a battery pack that prevents a solder material from flowing down due to a tab electrically connecting a battery to a protective circuit board, thereby improving the reliability, coupling efficiency, safety, and productivity of the battery pack.
2. Description of the Related Art
Recently, compact and light portable electric and electronic appliances, such as cellular phones, laptop computers, camcorders, are being actively developed and produced. Battery packs are embedded in the portable appliances respectively to operate the portable appliances even in places where separate power sources cannot be provided. Considering cost, the battery packs are recently employing chargeable and dischargeable batteries. The batteries include nickel-cadmium (Ni—Cd) batteries, nickel-metal hydride (Ni-MH) batteries, lithium batteries, and lithium ion secondary batteries.
In particular, the lithium ion secondary batteries are being widely employed as power sources of portable electronic appliances, and have operation voltages approximately three times as high as those of nickel-cadmium batteries and nickel-metal hydride batteries. They are also being widely employed due to their high energy density per weight.
Considering the consumption power and use time of a laptop computer that is representative of portable appliances, a plurality of lithium ion secondary cells are being arranged in series or in parallel in the laptop computer.
In this case, the lithium ion secondary cells for a laptop computer are embedded in a battery pack so as to attach or detach them to and from the laptop computer.
A protective circuit board for allowing or interrupting current flow is generally embedded in the battery pack to charge or discharge the battery pack, thereby preventing the lithium ion secondary cells from overheating, deteriorating, and exploding.
The protective circuit board is electrically connected to the lithium ion secondary cells through lead tabs, which correspond to a high current path through which charging and discharging currents of the lithium ion secondary cells flow.
In this case, the lead tabs are attached to the lithium ion secondary cells first, and then are electrically connected to the protective circuit board. The lead tabs are generally manually soldered to the protective circuit board. In this case, since the portions of the protective circuit board to which the lead tabs are soldered correspond to the high current path, the amount of a solder material used in the portions of the protective circuit board becomes larger that those in the other portions.
In other words, when the lead tabs are manually soldered to the protective circuit board, the amount of the solder material in the soldered portions of the protective circuit board becomes larger, in which case the solder material may disadvantageously flow down. Accordingly, the solder material flowing down along the protective circuit board may damage or cause the protective circuit board to malfunction due to a short circuit of the protective circuit board.
Moreover, when the protective circuit board coupled to the lithium ion secondary cells through the lead tabs is covered with a case to form the battery pack, the portions of the protective circuit board to which the lead tabs are coupled may be distorted or be erroneously assembled. In this case, it is necessary to solder the protective circuit board and the lead tabs again after removing the solder material, which increases manufacturing time and cost.
Furthermore, as the contact areas between the protective circuit board and the lead tabs become smaller, the amount of the solder material for coupling the lead tabs to the protective circuit board is also reduced, in which case the coupling forces between the protective circuit board and the lead tabs may weaken. The weak coupling forces between the protective circuit board and the lead tabs may cause the lead tabs to be separated from the protective circuit board. Furthermore, after long time use of the battery pack, the contact resistances between the protective circuit board and the lead tabs may increase due to cracking of the solder material, causing an increase in the internal resistance of the battery pack.